Known adjusting devices with a piezo drive, for example the linear drives known as "inch-worms", operate on the basis of the clamping principle. Such drives comprise three piezo elements, namely one linear piezo arranged parallel to the driven element and two clamping piezos that are positioned one at each end of the linear piezo and perpendicular to the driven element, and with one fixed in and the other movably supported in the housing.
While the application of an electrical voltage at the clamping piezos brings about a clamping of the driven member, such application at the linear piezo causes a movement of the movable clamping piezo. When this clamping piezo is in a clamped position on the driven element, but the fixed clamping piezo is not, then due to the clamping, the change in length of the linear piezo leads to a transmission of the movement to the driven element. If the fixed clamping piezo is activated and holds the driven element immobile, then when the functional connection of the movable clamping piezo is removed, a change in length of the linear piezo causes a resetting movement in preparation for the next transmission of motion.
In order to achieve a sure clamping and releasing and thus reliable operating performance, the clamping piezos in particular have very high requirements for precision. This effect is increased even more by the fact that piezo actuators in general are able to carry out positioning movements of only a few micrometers. However, since wear and deviations in length as a result of temperature and other environmental influences severely impair the clamping behavior, problems with the operating performance due to faulty or abrupt clamping are unavoidable.